Rex Ryan has made his share of mistakes trying to figure out the offense during his four-plus seasons as the Jets' coach, but this one may have trumped the rest.

How does he put Mark Sanchez in the fourth quarter of last night's game against the Giants after Geno Smith made it abundantly clear that he is not ready to be the starter heading into the regular season?

Why would Ryan subject Sanchez to injury, especially after Smith threw three interceptions and took a safety, showing the coach that he is not ready to be the No. 1 guy yet?

But after Smith departed the game after a fourth-quarter safety, there was Sanchez, hastily warming up and then going into a huddle of second- and third-string players, many of whom will not be with the team once the real games start.

It became immediately clear that this was a mistake on the very first play from scrimmage, when tackle Marvin Austin rushed through a gaping hole and sacked Sanchez for a 9-yard loss. A few minutes later, again under a heavy rush, Sanchez threw the ball to Mohamed Massaquoi. And just after he delivered the pass, Austin crashed in again, this time leveling Sanchez.

He grabbed his right shoulder -- his throwing shoulder -- and winced in pain. He came to the sideline and was examined, trying to shake off the pain but mostly failing. Then he angrily took off his helmet, unfastening the chinstrap with his left hand. He couldn't raise his right arm to take off his jersey and shoulder pads, needing help from others to remove his equipment.

Afterward, a testy Ryan took full responsibility for the decision to play Sanchez, with the coach explaining that this was about winning the game, about competing, and that this sort of thing happens in football.

But it never should have happened. Not after Ryan saw Smith throw three interceptions and fail to seize the opportunity to win a competition that up to this point was fairly even.

Smith had the chance to put away Sanchez, but instead he played his way out of the competition. But now the Jets might have no choice but to turn to the rookie if Sanchez's shoulder injury is serious. Ryan said afterward that the team didn't know the severity of the injury.

Did Sanchez win by default and then lose by knockout?

Only the Jets . . . only the Jets.

They'd better hope Sanchez wasn't seriously injured, or this will turn into yet another sad chapter in the team's mostly sad history.

Say what you want about Sanchez and hisviability -- or lack thereof -- as the Jets' starter. But the fact remains that he was the one who gave the team its best chance to win heading into the season.

Before this, anyway.

Ryan -- and only Ryan -- is the one to take the blame for this one, though. He said it was his call to put Sanchez in the game, even though common sense suggested that there was no way Sanchez should have gone anywhere near the field. Especially with the rag-tag group in the game on both sides of the ball. If Ryan wanted to see the competition between the two quarterbacks continue, how do you get an accurate assessment when one of the guys is playing alongside some teammates who won't even be here next week?

Ryan understood that he'd be second-guessed after Sanchez suffered the injury, but what about the first guess? What about the absurdity of putting him in the game in the first place?

Ryan should have used simple logic in this case. With Smith showing he wasn't ready for prime time, Ryan needed to take it upon himself to keep Sanchez from subjecting himself to unnecessary injury.

It's one thing if Sanchez had been playing behind the first-team offensive line. But Ryan had pulled almost all his starters before putting in Sanchez.

And now Ryan might have to pay dearly for it if Sanchez's injury is more serious than a bruise.

He made one gigantic mistake by putting his presumptive starting quarterback in harm's way.